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United States Patent |
6,192,299
|
Kubota
,   et al.
|
February 20, 2001
|
Method of measuring operation characteristic of proportional
electromagnetic control valve, method of controlling operation of
hydraulic cylinder, and method of modifying operation characteristic of
proportional electromagnetic control valve
Abstract
A method by which an operation characteristic of a proportional
electromagnetic control valve can be automatically measured in a short
period of time. For this purpose, in the operation characteristic
measuring method of the present invention, when the proportional
electromagnetic control valve to be measured is a proportional
electromagnetic pressure control valve, at each step for measuring a
pressure of a hydraulic circuit, the pressure is measured with a
predetermined interval of time, the pressure is assumed to be stabilized
at a point of time when a difference .DELTA.P between the measured
pressure value and the previously measured pressure value becomes a
predeterminied level or less, and the measured pressure value at this
point of time is employed as a pressure corresponding to a load current at
this step. The present invention is used at the time when an injection
molding machine is inspected at its manufacturing site upon shipping and
at the time when the injection molding machine is controlled while being
actually operated.
Inventors:
|
Kubota; Koji (Aichi-ken, JP);
Ikarashi; Masaaki (Aichi-ken, JP);
Miyagawa; Satoshi (Aichi-ken, JP)
|
Assignee:
|
Mitsubushi Heavy Industries, Ltd. (Tokyo, JP)
|
Appl. No.:
|
021414 |
Filed:
|
February 10, 1998 |
Foreign Application Priority Data
Current U.S. Class: |
700/282; 700/204; 700/301; 700/304; 702/96; 702/98 |
Intern'l Class: |
G05D 007/06 |
Field of Search: |
700/282,301,304,197,200,203,204
702/94,96,97,98,138,149
|
References Cited
U.S. Patent Documents
3626384 | Dec., 1971 | Davis | 702/195.
|
4720807 | Jan., 1988 | Ferran et al. | 700/282.
|
4734869 | Mar., 1988 | Mickowski | 702/183.
|
5040126 | Aug., 1991 | Allington | 702/47.
|
5595693 | Jan., 1997 | Fujita et al. | 264/40.
|
5916501 | Jun., 1999 | Hehl | 264/40.
|
5918195 | Jun., 1999 | Halgrimson et al. | 702/94.
|
6108587 | Aug., 2000 | Shearer et al. | 700/200.
|
Foreign Patent Documents |
WO 97/02940 | Jan., 1997 | DE | .
|
64-9177 | Feb., 1989 | JP.
| |
5-57777 | Mar., 1993 | JP.
| |
6-281043 | Oct., 1994 | JP.
| |
Other References
Translations of parts of Backe, W.; Grundiagen und Entwickiungstendenzen in
der Ventiltechnik, in: o + p, Olhydraulik und Pneumatik, 34 (1990), pp.
498-504.
Translation of passages of reference Edelmann, H.: Schneile
Proportionalventile und ihre Anwendung, in: o + p, Olhydraulik und
Pneumatik 30 (1986) pp. 35-40.
|
Primary Examiner: Grant; William
Assistant Examiner: Rodriguez; Paul
Attorney, Agent or Firm: Armstrong, Westerman, Hattori, McLeland & Naughton
Claims
What is claimed is:
1. A method of correcting operational characteristics of a proportional
electromagnetic control valve of a hydraulic circuit, in accordance with
an optimum value corresponding to a load current value of the proportional
electromagnetic control valve and in a memory in the form of a
characteristic curve, to normalize a possible unsatisfactory operation of
a hydraulic cylinder of the hydraulic circuit, said method comprising
(a) designating an arbitrary hydraulic pressure or flow rate of the
hydraulic circuit;
(b) reading out, from the characteristic curve in the memory, an initial
electric load current value for the proportional electromagnetic control
valve corresponding to a level of said designated pressure or flow rate;
(c) loading said read out initial electric current to the proportional
electromagnetic control valve;
(d) measuring an actual pressure or flow rate of the hydraulic circuit
corresponding to said loaded electric current;
(e) reading out, from the characteristic curve in the memory, an on-curve
electric load current value, for said proportional electromagnetic control
valve, corresponding to said measured actual pressure or flow rate value
from said characteristic curve in the memory as an electric current value.
(f) calculating a difference between said initial electric load current
value readout by the first-named reading and said actual electric load
current value read out by the second-named reading;
(g) adding or subtracting said calculated difference to or from said
initial load current level to obtain a target electrical load current
value; and
(h) updating the characteristic curve in the memory to such a
characteristic curve that said obtained target electrical load current
value is treated as said initial electrical load current value
corresponding to said designated pressure or flow rate.
2. A method of measuring an operation characteristic of a proportional
electromagnetic control valve, in a hydraulic circuit which actuates a
hydraulic cylinder, the control valve being, operable to control a
hydraulic pressure and a flow rate based on a load of electrical current
for the control valve, said method comprising the steps of:
if the proportional electromagcnetic control valve is a proportional
electromagnetic pressure control valve for controlling a pressure of the
hydraulic cylinder
(a) cutting off a flow of the hydraulic circuit into the cylinder;
(b) successively loading a predetermined series of electrical currents for
the proportional electromagnetic pressure control valve;
for each of said loaded electrical currents,
(c) measuring a pressure of the hydraulic circuit at regular time
intervals;
(d) calculating a difference in pressure between a then-current measured
pressure and a preceding measured pressure;
(e) repeating said steps (c) and (d) until such pressure difference becomes
smaller than a predetermined reference value; and
when said pressure difference becomes smaller than a predetermined
reference value,
(f) defining said measured hydraulic pressure corresponding to said loaded
electrical current as the operation characteristic of said proportional
electromagnetic pressure control valve with respect to pressure-electric
current.
3. A method of measuring an operation characteristic of a proportional
electromagnetic control valve, in a hydraulic circuit which actuates a
hydraulic cylinder, the control valve being operable to control a
hydraulic pressure and a flow rate based on a load of electrical current
for the control valve, said method comprising the steps of
if the proportional electromagnetic control valve is a proportional
electromagnetic flow control valve for controlling a flow rate of the
hydraulic cylinder,
(a) successively loading different magnitudes of electrical current for the
proportional electromagnetic flow control valve;
for each of said different magnitudes of electrical currents,
(b) actuating the hydraulic cylinder by the flow control valve in
accordance with said loaded electrical current;
(c) measuring a distance by which a hydraulic ram of the hydraulic cylinder
has been moved in a predetermined time as the result of said actuating in
step (b);
(d) calculating a velocity of the hydraulic ram of the cylinder using said
measured distance; and
(e) obtaining a velocity-electric current characteristic of said
proportional electromagnetic flow control valve based on said loaded
magnitude of electrical current and the calculated velocity of the ram.
4. A method for controlling a hydraulic cylinder which is actuated by a
hydraulic circuit, a proportional electromagnetic control valve in the
hydraulic circuit being operable to control a hydraulic pressure and a
flow rate based on a load of electrical current for the control valve,
said method comprising the steps of:
if the proportional electromagnetic control valve is a proportional
electromagnetic pressure control valve for controlling a pressure of the
hydraulic cylinder,
(a) cutting off a flow of the hydraulic circuit into the cylinder,
(b) successively loading a predetermined series of electrical currents for
the proportional electromagnetic pressure control valve;
for each of said loaded electrical currents.
(c) measuring a pressure of the hydraulic circuit at regular time
intervals;
(d) calculating a difference in pressure between the then-current measured
pressure and a preceding measured pressure;
(e) repeating said steps (c) and (d) until such pressure difference becomes
smaller than a predetermined reference value;
when said pressure difference becomes smaller than a predetermined
reference value,
(f) defining said measured hydraulic pressure, corresponding to said loaded
electrical current, as the operation characteristic of said proportional
electromagnetic pressure control valve with respect to pressure-electric
current;
(g) storing in a memory said defined pressure-electric current
characteristic of said proportional electromagnetic pressure control
valve;
in an actual operation of the hydraulic cylinder,
(h) designating a target pressure of the hydraulic cylinder,
(i) selecting, from said pressure-electric current characteristic stored in
the memory, an electric load current corresponding to the target pressure;
and
(j) loading said selected electric load current to said proportional
electromagnetic pressure control valve so as to control said hydraulic
cylinder.
5. A method for controlling a hydraulic cylinder which is actuated by a
hydraulic circuit, a proportional electromagnetic control valve in the
hydraulic circuit being operable to control a hydraulic pressure and a
flow rate based on a load of electrical current for the control valve,
said method comprising the steps of:
if the proportional electromagnetic control valve is a proportional
electromagnetic flow control valve for controlling a flow rate of the
hydraulic cylinder,
(a) successively loading different magnitudes of electrical current for the
proportional electromagnetic flow control valve;
for each of said different magnitudes of electrical currents,
(b) actuating the hydraulic cylinder by the flow control valve in
accordance with said loaded electrical current;
(c) measuring a distance by which a hydraulic ram of the hydraulic cylinder
has been moved in a predetermined time as the result of said actuating
time in step (b);
(d) calculating a velocity of the hydraulic ram of the cylinder based on
said measured distance;
(e) obtaining a velocity-electric current characteristic of said
proportional electromagnetic flow control valve based on said magnitude of
electrical current and the calculated velocity of the ram;
(f) storing in a memory said obtained velocity-electric current
characteristic of said proportional electromagnetic flow control valve;
in an actual operation of the hydraulic cylinder,
(g) designating a target velocity of the hydraulic ram;
(h) selecting, from said velocity-electric current characteristic stored in
the memory, an electric load current corresponding to the desired
velocity; and
(i) loading said selected electric load current to said proportional
electromagnetic flow control valve so as to control said hydraulic
cylinder.
6. A method for controlling a hydraulic cylinder which is actuated by a
hydraulic circuit, a proportional electric control valve in the hydraulic
circuit being operable to control a hydraulic pressure and a flow rate
based on a load of electrical current for the control valve, said method
comprising the steps of:
if the proportional electromagnetic control valve is a proportional
electuomagnietic pressure control valve for controlling a pressure of the
hydraulic cylinder,
(a) cutting off a flow of the hydraulic circuit into the cylinder,
(b) successively loading a predetermined series of electrical currents lor
the proportional electromagnetic pressure control valve;
for each of said loaded electrical currents,
(c) measuring a pressure of the hydraulic circuit at regular time
intervals;
(d) calculating a difference in pressure between the then-current measured
pressure and a preceding measured pressure;
(e) repeating said steps (c) and (d) until such pressure difference becomes
smaller than a predetermined reference value;
when said pressure difference becomes smaller than a predetermined
reference value;
(f) defining said measured hydraulic pressure, corresponding to said loaded
electrical current, as the operation characteristic of said proportional
electromagnetic pressure control valve with respect to pressure-electric
current;
(g) creating a table of said defined operation characteristic of
pressure-electric current;
(h) calculating a function based on said created table;
(i) storing in a memory said function calculated in said step (g);
in an actual operation of the hydraulic cylinder,
(j) reading said stored function;
(k) calculating, based on said read function, an electric current
corresponding to a given target pressure value; and
(l) loading said electric current, which is calculated in said step (j), to
said proportional electromagnetic pressure control valve so as to control
said hydraulic cylinder.
7. A method for controlling a hydraulic cylinder which is actuated by a
hydraulic circuit, a proportional electromagnetic control valve in the
hydraulic circuit being operable to control a hydraulic pressure and a
flow rate based on a load of electrical current for the control valve,
said method comprising the steps of:
if the proportional electromagnetic control valve is a proportional
electromagnetic flow control valve for controlling a flow rate of the
hydraulic cylinder,
(a) successively loading different magnitudes of electrical current for the
proportional electromagnetic flow control valve;
for each of said different magnitudes of electrical current,
(b) actuating the hydraulic cylinder by the flow control valve in
accordance with said loaded electrical current;
(c) measuring a distance by which a hydraulic ram of the hydraulic cylinder
has been moved in a predetermined time as the result of said actuating in
step (b);
(d) calculating a velocity of the hydraulic ram of the cylinder based on
said measured distance; and
(e) obtaining a velocity-electric characteristic of said proportional
electromagnetic flow control valve based on said loaded magnitude of
electrical current and the calculated velocity of the ram;
(f) creating a table of said obtained velocity-electric current
characteristic;
(g) calculating a function based on the table created in step (f);
(h) storing in a memory said function calculated in step (g);
in an actual operation of the hydraulic cylinder,
(i) reading said stored function;
(j) calculating, based on said read function, an electric current
corresponding to a given target velocity value of the hydraulic ram; and
(k) loading said electric current, which is calculated in said step (j), to
said proportional electromagnetic flow control valve so as to control said
hydraulic cylinder.
Description
BACKGROUND OF THE INVENTION
1) Field of the Invention
This invention relates to a method of actually measuring a pressure-current
characteristic as an operation characteristic of a proportional
electromagnetic control valve in a hydraulic circuit or a velocity-current
characteristic of a hydraulic cylinder; a method of controlling, based on
thus measured result, an operation state of the hydraulic cylinder; and a
method of modifying a prestored operation characteristic. In particular,
the present invention relates to a method of measuring an operation
characteristic of a proportional electromagnetic control valve, a method
of controlling an operation of a hydraulic cylinder, and a method of
modifying an operation characteristic of the proportional valve which are
suitably used when an injection molding machine is inspected at its
manufacturing site upon shipping or when the injection molding machine is
controlled while being actually operated.
2) Description of the Related Art
In an injection molding machine, while a hydraulic pressure from a
hydraulic pump or accumulator is supplied to a hydraulic cylinder
(injection cylinder, closing cylinder, nozzle tcuch cylinder, or the like)
via a proportional electromagnetic control valve (proportional
electromagnetic flow control valve or proportional electromagnetic
pressure control valve) so as to control velocity or pressure, such a
proportional electromagnetic control valve yields a large fluctuation in
its characteristic in general.
Consequently, prior to shipment of an injection molding machine, its
hydraulic circuit is operated in the actual machine, several points of
pressure levels or flow levels of its proportional electromagnetic control
valve with respect to its load current are measured, thus measured levels
are compared with a reference characteristic attached to the proportional
electromagnetic control valve, and the gain of the load current output
circuit for the proportional electromagnetic control valve is manually
adjusted before shipping. Inmost cases, however, only the maximum and
minimum levels are measured for output current adjustment and, also under
the influence of differences among machines and circuit configurations,
thus modified characteristic may not have a high accuracy.
Japanese Patent Publication No. SHO 64-9177 discloses a technique in which,
in order to enhance accuracy of an actually employed characteristic, the
characteristic of a proportional electromagnetic control valve built in an
injection molding machine is actually measured before shipping its
hardware, a correction characteristic table providing a relationship
between an ordered level and an output level is prepared according to the
measured result, and the proportional electromagnetic valve is controlled
with reference to the contents of this correction characteristic table
upon actually operating the hardware.
In the characteristic auto-modifying technique for a proportional
electromagnetic control valve disclosed in the above-mentioned
publication, the proportional electromagnetic control valve is operated
with its input levels successively changing from the minimum input level
to maximum input level so that their corresponding numeral output levels
are initially measured and, according to a result of a comprehended
relationship between these numerous actually measured levels and their
corresponding ordered levels, the correction characteristic table is
prepared such that the output level is proportional to the input level.
In such a technique for measuring the characteristic of a proportional
electromagnetic control valve, while numerous points from the minimum
input level to the maximum input level are actually measured and plotted
when preparing the correction characteristic table, there may be cases
where, due to the condition under which a hydraulic cylinder is used and
the like, the maximum pressure or maximum velocity cannot be attained in
the state where the proportional electromagnetic control valve is built in
the machine. In such a case, the characteristic of the proportional
electromagnetic valve cannot be modified. Also, the number of measuring
points may be so large that an enormous amount of labor and time is
necessitated.
Theretfore, Japanese Patent Application Laid-Open (Kokai) No. HEI 5-57777
discloses a technique in which reference characteristic curve data of a
proportional electromagnetic control valve of the same type as that of the
proportional electromagnetic control valve built in the machine are
prestored in a storage circuit in a microcomputer in a control unit of the
injection molding machine, the microcomputer causes the proportional
electromagnetic control valve to operate (in a test run) by given ordered
levels at predetermined two points, output (pressure or velocity) levels
corresponding thereto are respectively measured, and then, according to
the two points of ordered levels and output levels obtained by the test
run and the above-mentioned reference characteristic curve data, output
levels corresponding to individual points on the reference characteristic
curve are successively computed to recompose the characteristic curve.
In the technique in which the actually measured level and the reference
characteristic table attached to the proportional electromagnetic control
valve are compared with each other, and the maximum and minimum levels are
regulated by gain adjustment of a load current output circuit amplifier of
the proportional electromagnetic control valve so as to modify
characteristic levels of the proportional electromagnetic control valve,
as mentioned above, however, data of proportional electromagnetic control
valve differ among different machines and, also under the influence of
differences in circuit configurations, a linearity may not be obtained
between the ordered and executed levels, thus deteriorating the accuracy
of the modified characteristic.
In the technique in which a characteristic is actually measured, a
correction characteristic table keeping a relationship between ordered and
output levels is prepared, and a correction characteristic is added so as
to control the proportional electromagnetic control valve as disclosed in
Japanese Patent Publication No. 64-9177, numerous points from the minimum
input level to maximum input level must be actually measured to prepare
the correction characteristic table as mentioned above. Here, since the
number of measured points is large, an enormous amount of labor and time
is necessary.
In the method disclosed in Japanese Patent Application Laid-Open (Kokai)
No. HEI 5-57777 in which characteristic data of the proportional
electromagnetic control valve are obtained on the analogy of two points of
data, correct data may not be obtained from the two points alone since the
original data are a curve constituted by a polynomial function.
In the foregoing method in which a data table is retrieved, an accurate
resolution as fine as 0.1% cannot be obtained.
In the conventional pressure measurement in an actual hydraulic circuit, in
the case where pressure is relatively low, the pressure is measured after
a rising overshoot upon switching hydraulic pressure is suppressed. When
the number of measuring points is large, however, it takes much time
therefor. When measuring velocity, since time by which a predetermined
position travels a predetermined distance is measured to determine the
velocity. Accordingly, it takes much time for measurement at the minimum
velocity, and an enormous amount of time is required for measuring
numerous points.
SUMMARY OF THE INVENTION
In view of such problems, it is a first object of the present invention to
provide a method of measuring an operation characteristic of a
proportional electromagnetic control valve, which allows the operation
characteristic to be automatically measured in a short period of time,
thus shortening the time required for inspection upon shipment.
It is a second object of the present invention to provide a method of
controlling an operation of a hydraulic cylinder, which allows the
hydraulic cylinder to be controlled constantly at a high accuracy
according to the automatically measured operation characteristic.
It is a third object of the present invention to provide a method of
modifying an operation characteristic of a proportional electromagnetic
control valve, which allows an operation characteristic kept in a memory
to be automatically modified after shipping the machine, so that the
operation characteristic matching the present state can always be
maintained.
In order to achieve the above-mentioned objects, the method of measuring an
operation characteristic of a proportional electromagnetic control valve
in accordance with the present invention is, in a hydraulic circuit in
which a hydraulic cylinder is operated as a proportional electromagnetic
control valve which adjusts hydraulic pressure and flow rate, when the
proportional electromagnetic control valve is a proportional
electromagnetic pressure control valve which controls a hydraulic pressure
in response to a load current, a method of measuring a pressure-current
characteristic as the operation characteristic of the proportional
electromagnetic pressure control valve by successively changing the load
current with respect to the proportional electromagnetic pressure control
valve stepwise and measuring a pressure of the hydraulic circuit
corresponding to the load current at each step in a closed operation state
of the hydraulic circuit; wherein, at each step for measuring the pressure
of the hydraulic circuit, the pressure is measured at a predetermined
interval of time, the pressure is assumed to be stabilized at a point of
time when a difference between the measured pressure value and the
previously measured pressure value becomes a predetermined level or
smaller, and the measured pressure value at this point of time is employed
as the pressure corresponding to the load current at this step.
In the method of measuring an operation characteristic of a proportional
electromagnetic control valve in accordance with the present invention
mentioned above, even in the case where pressure is relatively low, a
pressure obtained when the inclination of a declining curve of rising
overshoot upon switching hydraulic pressure becomes a predetermined level
or smaller is employed as the measured value, whereby the measurement time
can be shortened. Accordingly, even when numerous points are measured, the
period of time for measuring the operation characteristic can be reduced,
thus allowing the time required for the inspection upon shipping or the
like to greatly decrease.
Also, the method of measuring an operation characteristic of a proportional
electromagnetic control valve in accordance with the present invention is,
in a hydraulic circuit in which a hydraulic cylinder is operated as a
proportional electromagnetic control valve adjusts hydraulic pressure and
flow rate, when the proportional electromagnetic control valve is a
proportional electromagnetic flow control valve which controls a flow rate
in response to a load current, a method of measuring a velocity-current
characteristic as the operation characteristic of the proportional
electromagnetic flow control valve by causing the hydraulic cylinder to
attain an operable state, successively changing the load current with
respect to the proportional electromagnetic flow control valve stepwise so
as to operate the hydraulic cylinder, and computing a velocity of a
hydraulic ram of the hydraulic cylinder corresponding to the load current
at each step; wherein, at each step for computing the velocity of the
hydraulic ram, a traveling distance of the hydraulic ram by a
predetermined period of time is measured, and a velocity computed
according to the traveling distance is employed as the velocity
corresponding to the load current at this step.
In the above-men-ioned method of measuring an operation characteristic of a
proportional electromagnetic control valve in accordance with the present
invention, the traveling distance for a predetermined time is measured so
as to determine the velocity, thus allowing the measuring time to become
shorter as compared with the conventional method, in particular, on the
minimum velocity side. Accordingly, even when numerous points are
measured, the period of time for measuring the operation characteristic
can be reduced, thus allowing the time required for the inspection upon
shipping or the like to greatly decrease.
The method of controlling an operation of a hydraulic cylinder in
accordance with the present invention is a method of controlling an
operation state of the hydraulic cylinder by adjusting hydraulic pressure
and flow rate by a hydraulic circuit having a proportional electromagnetic
control valve; wherein an operation characteristic of the proportional
electromagnetic control valve is measured by one of the above-mentioned
two methods of measuring an operation characteristic of a proportional
electromagnetic control valve and is stored into a memory and, when
specifying a hydraulic pressure to the hydraulic cylinder or a velocity of
the hydraulic ram of the hydraulic cylinder, an operation characteristic
value matching thus specified level is read out from the memory and is
converted into an executive current, which is then applied to the
proportional electromagnetic control valve so as to control the operation
state of the hydraulic cylinder.
In the above-mentioned method of controlling an operation of a hydraulic
cylinder in accordance with the present invention, when the hydraulic
pressure of the hydraulic cylinder or the velocity of the hydraulic ram is
specified at the time of actual operation, the current characteristic
value matching thus specified level is read out from the memory and is
converted into an executive current so as to be applied to the
proportional electromagnetic control valve, whereby the operation state of
the hydraulic cvlinder is controlled. Therefore, according to the
automatically measured operation characteristic, the hydraulic cylinder
can be always controlled with a high accuracy.
Also, the method of controlling an operation of a hydraulic cylinder in
accordance with the present invention is a method of controlling an
operation state of the hydraulic cylinder by adjusting hydraulic pressure
and flow rate by a hydraulic circuit having a proportional electromagnetic
control valve; wherein an operation characteristic of the proportional
electromagnetic control valve is measured by one of the above-mentioned
two methods of measuring an operation characteristic of a proportional
electromagnetic control valve and is stored in a memory, a table for
relating a load current level to the measured operation characteristic
value at each step is prepared, interpolation is performed between points
plotted on the table so as to determine a continuous function, which is
then stored into a memory as the operation characteristic of the
proportional electromagnetic control valve, the function is read out from
the memory upon actual operation of the hydraulic cylinder, an executive
current level is computed according to the function and a target level for
hydraulic pressure to the hydraulic cylinder or velocity of a hydraulic
ram of the hydraulic cylinder, and a current corresponding to the
executive current level is applied to the proportional electromagnetic
control valve so as to control the operation state of the hydraulic
cylinder.
In the method of controlling an operation of a hydraulic cylinder in
accordance with the present invention, the operation characteristic stored
in the memory as a function is automatically modified and rewritten in
response to a request for automatic modification. Consequently, even when
the proportional electromagnetic control valve built in the hydraulic
circuit or functional parts relating to hydraulic pressure or flow rate
are repaired or exchanged, the operation characteristic of the
proportional electromagnetic control valve stored in the memory can be
automatically modified while the machine is kept installed as it is, and
the hydraulic cylinder can always be controlled with a high accuracy
according to thus automatically modified operation characteristic.
Further, the method of modifying an operation characteristic of a
proportional electromagnetic control valve in accordance with the present
invention is, when, in order to control an operation state of a hydraulic
cylinder by adjusting hydraulic pressure and flow rate by a hydraulic
circuit having a proportional electromagnetic control valve, an operation
characteristic value corresponding to a load current level of the
proportional electromagnetic control valve is prestored into a memory as a
characteristic curve, a method of modifying the characteristic curve
stored in the memory; wherein a hydraulic pressure or flow rate of the
hydraulic circuit is specified, a load current level of the proportional
electromagnetic control valve corresponding to thus specified level is
read out from the characteristic curve in the memory, a current
corresponding to thus read-out load current level is applied to the
proportional electromagnetic control valve, the pressure or flow rate of
the hydraulic circuit corresponding to this current is actually measured,
a load current level of the proportional electromagnetic control valve
corresponding to thus actually measured value is read out from the
characteristic curve in the memory, a difference between thus obtained
load current level and an initial load current level is added to or
subtracted from the initial load current level, and a current level
resulting from this adding or subtracting operation is written into the
memory as a modified load current level corresponding to the specified
level so as to modify the load current level of the characteristic curve
in the memory.
In the above-mentioned method of modifying an operation characteristic of a
proportional electromagnetic control valve in accordance with the present
invention, in the case where an operation characteristic value
corresponding to the load current level of the proportional
electromagnetic control valve is prestored in the memory as a
characteristic curve, the characteristic curve (operation characteristic)
can be automatically modified after shipping the machine. Accordingly,
even when the proportional electromagnetic control valve built in the
hydraulic circuit or functional parts relating to hydraulic pressure or
flow rate are repaired or exchanged, the operation characteristic
corresponding to the current state can always be held in the memory while
the machine is kept installed as it is.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view for explaining a method of measuring an operation
characteristic of a proportional electromagnetic pressure control valve in
accordance with one embodiment of the present invention;
FIG. 2 is a graph showing a rising state of hydraulic pressure in a
hydraulic circuit of this embodiment;
FIG. 3A is a lateral sectional view schematically showing an injection
cylinder in order to explain a technique for measuring velocity of a
conventional injection ram;
FIG. 3B is a lateral sectional view schematically showing an injection
cylinder in order to explain a method of measuring an operation
characteristic of a proportional electromagnetic flow control valve
(technique for measuring velocity of an injection ram) in this embodiment;
FIG. 4 is a view showing a configuration of the hydraulic circuit and
control system in an injection molding machine in accordance with this
embodiment;
FIG. 5 is a block diagram functionally showing a detailed configuration of
the hydraulic circuit and control system in order to explain a method of
controlling an operation of an injection cylinder (method of modifying an
operation characteristic of a proportional electromagnetic pressure
control valve) in this embodiment; and
FIG. 6 is a view for explaining another example of method of modifying an
operation characteristic of a proportional electromagnetic pressure
control valve in accordance with this embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the following, an embodiment of the present invention will be explained
with reference to the accompanying drawings.
Explained in this embodiment is a case where the present invention is
applied to a hydraulic operation control circuit for an injection molding
machine, which comprises a hydraulic pump, a switching valve, and the
like, and adjusts hydraulic pressure and flow rate so as to operate the
hydraulic cylinder, as will be explained later, thereby performing a
closing operation, injection of melted resin, and the like.
First, with reference to FIG. 4, the configuration of the hydraulic circuit
and control system of the injection molding machine to which the method of
the present invention is applied will be explained. Depicted in FIG. 4 are
an injection cylinder (hydraulic cylinder) 1 of the injection molding
machine whose operation is to be controlled in this embodiment, an
injection ram (hydraulic ram) 2 within the injection cylinder 1, and an
injection screw 2a connected to the injection ram 2.
Also depicted are a position sensor 3 for detecting an amount of movement
of the injection ram 2, a direction-switching valve 4 for turning on/off
an injecting operation of the injection cylinder 1, a proportional
electromagnetic flow control valve (proportional electromagnetic control
valve) 5 for controlling the flow rate of a hydraulic operating fluid to
the injection cylinder 1 in response to a load current from a control unit
12, a proportional electromagnetic pressure control valve (proportional
electromagnetic control valve) 6 for controlling the pressure of the
hydraulic operating fluid in response to a load current from the control
unit 12, a continuous flow pump 7 which is driven by a motor (M) 7a so as
to rotate at a predetermined rpm, a check valve 8, and a pressure sensor 9
for detecting pressure in this hydraulic circuit.
The above-mentioned direction-switching valve 4, control valves 5 and 6,
pump 7, check valve 8, and the like constitute the hydraulic circuit for
operating the injection cylinder 1 at an injecting process caused by the
injection screw 2a.
On the other hand, provided are an operation panel 11 for setting and
inputting various kinds of information such as specified levels (control
target levels) for pressure of the hydraulic circuit, velocity of the
injection ram 2 (flow rate of the hydraulic circuit), and the like to the
control unit 12 explained later, and the control unit 12, which receives
signals from the position sensor 3 and pressure sensor 9 and applies a
load current to each of the control valves 5 and 6 so as to control the
hydraulic circuit, thereby controlling the operation state of the
injection cylinder 1. The control unit 12 is constituted by, in addition
to a CPU 13 as an arithmetic processing unit, a memory 14, a D/A converter
15, an output amplifier 16, and an A/D converter 17 which are built
therein.
Here, the CPU 13 actually controls an operation state of the injection
cylinder 1 in addition to measuring/modifying operation characteristics of
the control valves 5 and 6, which will be explained later; whereas the
memory 14 stores the operation characteristics of the control valves 5 and
6, as will be explained later.
On the other hand, the D/A converter 15 converts, from digital to analog,
control signals (load current level signals) sent from the CPU 13 for the
respective control valves 5 and 6. The amplifier (output amplifier) 16
amplifies the control signals from the D/A converter 15 and outputs the
amplified signals to their corresponding control valves 5 and 6. The A/D
converter 17 converts analog detection signals from the position sensor 3
and pressure sensor 9 into digital signals and outputs thus converted
signals to the CPU 13.
Explained in the following with reference to FIGS. 1 to 3 is a method of
automatically inspecting, in a working manner, a pressure-current
characteristic (operation characteristic) of the proportional
electromagnetic pressure control valve 6 or the relationship between
velocity of the injection cylinder 1 and the load current level to the
proportional electromagnetic flow control valve 5 [a velocity-current
characteristic of the injection cylinder 1, and an operation
characteristic (flow rate-current characteristic) of the proportional
electromagnetic flow control valve 5] when the injection molding machine
equipped with the hydraulic circuit and control unit 12 of this embodiment
constructed, as mentioned above, is inspected upon shipment in he site
where the machine is manufactured.
FIG. 2 is a graph showing a rising state of hydraulic pressure in the
hydraulic circuit of this embodiment. It illustrates a result obtained
when, in this embodiment, the hydraulic pump 7 is driven, the injection
cylinder 1 is operated under hydraulic pressure, the injection ram 2 of
the injection cylinder 1 in the actual machine is pressed into the end
portion of the stroke for closing, melted resin injection, and the like
such that the hydraulic circuit attains a closed state, the load current
with respect to the proportional electromagnetic pressure control valve 6
is successively changed stepwise, and the pressure of the hydraulic
circuit is measured by the pressure sensor 9.
As shown in FIG. 2, in a low pressure band (Nos. 1 to 4), an overshoot
occurs in each step of measurement, and then pressure gradually converges
at the set pressure. Since it takes a certain time for pressure to
stabilize, a delay timer has conventionally been provided (see Ts in FIG.
2 for its set level) to retard the pressure measuring timing. In such a
measuring technique, however, the measuring timing uniformly delays even
in the case where the set pressure is so high that pressure stabilizes in
a short time, whereby it takes an enormous amount of time to measure
pressure (measure an operation characteristic).
For measuring pressure in order to measure an operation characteristic in
this embodiment, upon measuring one step of pressure, as shown in the
pressure-declining curve after overshoot represented in FIG. 1, pressure
is repeatedly measured by the pressure sensor 9 at a constant time
interval t, the CPU 13 of the control unit 12 assumes pressure to be
stabilized when a difference .DELTA.P between the measured value and the
previously measured value becomes a sufficiently small constant numerical
value e or less, and this pressure is taken in as an operation pressure of
the proportional electromagnetic pressure control valve 6 corresponding to
the load current at this step.
Consequently, without necessitating a certain wait time Ts for each
measurement step before measurement as in the conventional case,
measurement is effected with a timing at which pressure is assumed to be
stabilized for each measurement step. Therefore, the pressure measurement
time requires only T.sub.1, thus allowing the operation pressure in the
next step to be measured after the time T.sub.1 is elapsed. Thus, the
total time required for preparing a pressure-current characteristic curve
in the CPU 13 of the control unit 12 can be made much shorter than that in
the conventional case.
Here, as shown in FIG. 2, overshoot hardly occurs in a high pressure band
(Nos. 5 to 7). Even in such a case, in the measuring method of this
embodiment, it is unnecessary to wait for the certain time Ts before
measurement in each measurement step, as mentioned above, whereby
measurement is effected with a timing T.sub.2 at which pressure is assumed
to be stabilized.
Meanwhile, FIG. 3A is a lateral sectional view schematically showing the
injection cylinder 1 for explaining a conventional technique for measuring
velocity of the injection ram 2; whereas FIG. 3B is a lateral sectional
view schematically showing the injection cylinder 1 for explaining a
method or measuring an operation characteristic of he proportional
electromagnetic flow control valve 5 (technique for measuring velocity of
the injection ram 2) in this embodiment.
When measuring an operation characteristic of the proportional
electromagnetic flow control valve 5, while the injection cylinder 1 of
the actual machine is set to an operable state, the load current to the
proportional electromagnetic flow control valve 5 is successively changed
stepwise, and the velocity of the injection ram 2 is measured while the
injection cylinder 1 is caused to operate.
Here, in the conventional technique shown in FIG. 3A, a time t by which the
injection ram 2 travels a predetermined distance 1.sub.O is measured so as
to compute a velocity 1.sub.O /t. In this embodiment, by contrast, as
shown in FIG. 3B, a distance x by which the injection ram 2 travels in a
predetermined time t.sub.O is precisely measured by means of the position
sensor 3 and is fed into the CPU 13 of the control unit 12, whereby the
velocity of the injection ram 2 is computed as x/t.sub.O. Then, the CPU 13
multiplies thus measured and computed velocity of the injection ram
(hydraulic ram) 2 by the pressure-receiving area of the injection cylinder
1 so as to compute a flow rate, and causes it to correspond to the load
current at each step, thereby forming a characteristic curve concerning
the flow rate-current characteristic of the proportional electromagnetic
flow control valve 5.
In the conventional technique shown in FIG. 3A, concerning the time for
traveling an approach distance m and the measurement distance 1.sub.o, in
particular when the current of the proportional electromagnetic flow
control valve 5 is low (flow rate is low), not only the measurement time
becomes longer, but also the time required for the hydraulic ram 2 to
return becomes longer. In the technique of the embodiment shown in FIG.
3B, by contrast, when the approach time and measurement time are
respectively set to 0.5 second and 1.5 seconds beforehand, for example,
the measurement time is always constant whether the current of the
proportional electromagnetic flow control valve 5 is high or low, thus
allowing the measurement to be completed in much shorter time than in the
conventional technique shown in FIG. 3A.
In this embodiment, according to the data measured by such a technique as
that mentioned above, characteristic curves for the proportional
electromagnetic flow control valve 5 and proportional electromagnetic
pressure control valve 6 are prepared, and thus prepared characteristic
curves are stored in the memory 14 of the control unit 12. In the case
where such a characteristic curve has already been stored in the memory
14, the characteristic curve in thememory 14 is rewritten ormodifiedbythe
characteristic curve prepared by the above-mentioned technique.
When the operating hydraulic pressure of the injection cylinder 1 or
velocity of the injection ram 2 in the injection molding machine is
specified upon actual adriving, the CPU 13 of the control unit 12 reads
out a current characteristic level corresponding to thus specified value
from the memory 14, converts thus read-out level to an executive current,
and applies this current to the proportional electromagnetic flow control
valve 5 and proportional electromagnetic pressure control valve 6 via the
D/A converter 15 and amplifier 16. As a result, the operation state of the
injection cylinder 1 is controlled so as to attain the specified value.
In the following, explanation will be provided for a method of modifying
the pressure-current characteristic of the proportional electromagnetic
pressure control valve 6 or flow rate-current characteristic of the
proportional electromagnetic flow control valve 5 thus written in the
memory 14. This embodiment encompasses two kinds of modifying method.
First and second examples thereof will be respectively explained with
reference to FIGS. 5 and 6.
FIG. 5 is a block diagram functionally showing a detailed configuration of
the hydraulic circuit and control system in order to explain a method of
controlling an operation of the injection cylinder 1 (method of modifying
an operation characteristic of the proportional electromagnetic pressure
control valve 6) in this embodiment. This process will be explained in
detail with reference to FIG. 5, additionally in view of the modifying and
rewriting function for the pressure characteristic in the proportional
electromagnetic pressure control valve 6 in the hydraulic circuit shown in
FIG. 4.
(1) When a request for automatically modifying the pressure characteristic
is issued from the operation panel 11 to the CPU 13 a pressure-specifying
level Pn stored in a memory (not depicted) built in a processing section
13a of the CPU 13 is sent to the memory 14, and a load current level In
corresponding to the pressure-specifying level Pn is read out from a
reference curve Ps of a pressure-current characteristic function table
stored in the memory 14 to the processing section 13a of the CPU 13 so as
to be temporarily kept there.
(2) According to a current (which corresponds to the current level In)
outputted from the processing section 13a of the CPU 13 via the D/A
converter 15 and amplifier 16, the proportional electromagnetic pressure
control valve 6 is operated, whereby the pressure of the hydraulic circuit
for driving the injection cylinder 1 is controlled. Then, an actual
pressure Pn' of the hydraulic circuit is measured by the pressure sensor
9, and thus measured signal is sent to an arithmetic section 13b of the
CPU 13 by way of the A/D converter 17. Here, the actual pressure Pn' is
measured by the technique previously explained with reference to FIG. 1.
(3) In the arithmetic section 13b of the CPU 13, according to the actual
pressure Pn' and the load current level In kept in the processing section
13a of the CPU 13 in the above-mentioned step (1), the actual pressure Pn'
is plotted on the pressure-current characteristic function table.
(4) As explained above as represented by the pressure-specifying level Pn,
pressure-specifying levels P.sub.1 to P.sub.MAX are successively fed to
the memory 14, current levels I.sub.1 to I.sub.MAX respectively
corresponding to the pressure-specifying levels are read out from the
characteristic curve Ps of the pressure-current characteristic function
table in the memory 14 to the processing section 13a of the CPU 13 so as
to be temporarily kept there, actual pressures P.sub.1 ' to P.sub.MAX ' of
the hydraulic pressure are fed to the arithmetic section 13b of the CPU 13
and successively plotted on the pressure-current characteristic function
table, and interpolation is made between thus plotted points, thereby
yielding a continuous actual pressure characteristic curve Pr as shown in
FIG. 5. Since this characteristic curve Pr has a form analogous to that of
the characteristic curve Ps in the initial reference characteristic
function table, the constant of function concerning the characteristic
curve Ps is modified so that the new characteristic curve Pr is adopted as
the function.
(5) In place of the function of the initial reference characteristic
function table, the new characteristic curve Pr is written into the memory
14 as a function, so as to be ready for actual operation. When controlling
actual operation, the CPU 13 uses the new function so as to determine a
load current level of the proportional electromagnetic pressure control
valve 6 corresponding to an arbitrary pressure-specifying level. Namely, a
target pressure or target ram velocity is set from the operation panel 11
so as to be transmitted to the CPU 13 of the control unit 12; whereas the
CPU 13 reads out the above-mentioned function from the memory 14, computes
a load current level corresponding to the target level according to the
function, and outputs a current corresponding to thus computed result via
the D/A converter 15 and amplifier 16, thus operating and controlling the
proportional electromagnetic pressure control valve 6 and proportional
electromagnetic flow control valve 5.
While a method of modifying an operation characteristic applied to the
proportional electromagnetic pressure control valve 6 is explained as an
example in the foregoing, a technique similar to that mentioned above is
applied to a case where an operation characteristic (flow rate-current
characteristic) of the proportional electromagnetic flow control valve 5
is to be modified.
On the other hand, FIG. 6 is a view for explaining the second example of
method of modifying an operation characteristic of the proportional
electromagnetic pressure control valve 6 in accordance with this
embodiment. Here, it is assumed that reference representative values of
the characteristic curve for pressure with respect to the load current
level of the proportional electromagnetic pressure control valve 6 (curve
referred to as Ps in FIG. 6), which are attached thereto by a maker of the
proportional electromagnetic pressure control valve, are prestored in the
memory 14 of the control unit 12 as being A/D converted.
Here, when a pressure Pa of the hydraulic circuit is specified from the
operation panel 11 to the CPU 13 in order to modify this characteristic
curve Ps, the CPU 13 reads out a load current level Ia corresponding to
this specified value Pa from the characteristic curve Ps stored in the
memory 14, and this Load current level Ia is D/A-converted by the D/A
converter 15 and, after being constantly amplified by the amplifier 16, is
outputted to the proportional electromagnetic pressure control valve 6.
Then, a pressure Pa' corresponding to this current level Ia is measured by
the pressure sensor 9, and thus actually measured value is fed to the CPU
13 after being converted from analog to digital by the A/D converter 17.
Here, the actually measured pressure value Pa' is determined according to
the technique previously explained with reference to FIG. 1.
The CPU 13 compares the actually measured pressure value Pa' with the
reference representative value Pa of the characteristic curve, replaces
the actually measured pressure value Pa' with the specified value, reads
out a current level Ia' corresponding to the actually measured value Pa'
from the reference representative characteristic curve Ps, adds (or
subtracts) a difference .DELTA.I between the current level Ia' and the
initial load current level Ia to (from) the initial load current level Ia,
and replaces a load current level Ib obtained as a result of this
arithmetic operation with the load current level of the reference
representative characteristic curve Ps, thus rewriting the memory 14.
In this manner, the current level of the characteristic curve Ps with
respect to a certain specified value can be modified.
As the foregoing technique is repeated while the magnitude of pressure is
changed, the characteristic curve Ps stored in the memory 14 is rewritten
into a modified characteristic curve Pr of pressure and current such as
that shown in FIG. 6 as dotted line.
When the characteristic curve approximates a line or when the difference
.DELTA.I is small, thus modified characteristic curve Pr has a practically
sufficient accuracy. Accordingly, the above-mentioned method of modifying
an operation characteristic can simply effect modification in the
manufacturing site or molding site, thus being quite convenient.
Though the method of modifying an operation characteristic applied to the
proportional electromagnetic pressure control valve 6 is explained as an
example in the foregoing, a technique similar thereto is applied to the
case where the operation characteristic (flow rate-current characteristic)
of the proportional electromagnetic flow control valve 5 is to be
modified.
Thus, in accordance with this embodiment, upon the shipping inspection at
the manufacturing site of the injection molding machine, the
pressure-current characteristic of the proportional electromagnetic
pressure control valve 6 or velocity-current characteristic of the
hydraulic cylinder 1 (flow rate-current characteristic of the proportional
electromagnetic flow control valve 5), which becomes a reference for
instructing and operating the hydraulic circuit, is automatically
inspected and modified in a working manner, whereby the executive value
corresponding to the specified value can be correctly reproduced, thus
making it possible to yield a correct resolution as fine as about 0.1%.
Also, even when the proportional electromagnetic control valves 5 and 6
built in the hydraulic circuit or functional parts relating to hydraulic
pressure and flow rate are repaired or exchanged, characteristics of the
proportional electromagnetic control valves 5 and 6 can be automatically
modified while the machine is kept installed as it is.
Since the load current level is modified such that the specified value and
the executive value coincide with each other and then is stored in the
memory 14 so as to be read out when necessary, the points of measurement
become less when the specified values are determined beforehand, thus
allowing the measurement time to become shorter.
Further, in the pressure measuring technique of this embodiment, even in
the case where pressure is relatively low, the pressure obtained when the
inclination of the declining curve of rising overshoot upon switching
hydraulic pressure becomes a predetermined level or less is employed as a
measured value, whereby the measurement time can be shortened. Also, in
the velocity measuring technique of this embodiment, since the distance of
travel in a predetermined time is measured so as to determine velocity,
measurement -ime can be made shorter than that in the conventional case,
in particular, on the minimum velocity side. Therefore, even when numerous
points are to be measured, time required for measuring an operation
characteristic can be greatly reduced.
As explained in the foregoing, in accordance with this embodiment, the
actually measured value is automatically modified to the specified value,
and the characteristic curves of the proportional electromagnetic control
valves 5 and 6 themselves are recomposed and stored in the memory 14. When
the actual machine is operated, the operation characteristics can be read
out from the memory 14 so as to control the proportional electromagnetic
control valves 5 and 6. Also, the shipping inspection can be effected in a
short time, whereas the characteristics can be automatically adjusted in a
molding factory after the machine is shipped.
Though the above-mentioned embodiment is explained with an example in which
the injection cylinder 1 is used; in a proportional electromagnetic
pressure control valve for controlling pressure of a closing cylinder, an
operation characteristic can also be modified by the same pressure
measuring method while the closing cylinder is set to a closed state.
Also, in a back-pressure proportional electromagnetic pressure control
valve, an operation characteristic can be modified in a method similar to
that mentioned above when pressure oil is supplied thereto while the
injection cylinder is set to a closed state.
Though the above-mentioned embodiment explains a case where the present
invention is applied to a hydraulic circuit for operating various kinds of
cylinders (injection cylinder and the like) in the injection molding
machine; without being restricted thereto, the present invention is also
applicable tc various kinds of apparatus where a hydraulic circuit for
operating a hydraulic cylinder is equipped with a proportional
electromagnetic control valve, whereby advantageous effects similar to
those mentioned above can be obtained.
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